PROJECT SUMMARY/ABSTRACT Development of tolerance to alcohol is thought to reflect a critical sign of problematic alcohol involvement, and is included as one of the diagnostic criteria for alcohol dependence in the DSM IV. Yet little is known of the relationship between tolerance development and levels of alcohol consumption, although it has been speculated that emergence of tolerance to aversive effects of ethanol may permit greater consumption, increasing alcohol exposure levels and concomitant problems. Exploring the relationship between ethanol tolerance and consumption is particularly critical during adolescence, with 12-21 yr. olds not only drinking substantially more per drinking occasion than adults, but also reporting a higher incidence of ethanol tolerance than any other age group. The studies outlined in this proposal will explore this relationship using a simple and well characterized animal model of adolescence in the rat, a model that is typified by 2-3 fold high levels of ethanol consumption, expression of markedly more acute tolerance (and under some instances, chronic tolerance), and an attenuated sensitivity to various aversive effects of alcohol when animals in this developmental phase are compared with adults. The proposed work will explore the development of acute and chronic tolerance to various aversive effects of ethanol and the relationships of these adaptations to ethanol consumption during the adolescent period and following comparable manipulations in adulthood. Neural systems influencing these adaptations and whether these adaptations are causal for elevated ethanol consumption during adolescence will also be explored. Work in this proposal will answer the following questions: What are the relationships among the emergence of acute, rapid and chronic tolerance for various aversive effects of ethanol in adolescents and adults (Sp.Aim 1)? Do chronic exposure regimens sufficient to induce chronic tolerance to these ethanol effects lead to increases in voluntary ethanol consumption in home cage and limited access tests, with this increased consumption being particularly marked in adolescence (Sp.Aim 2)? What role do NMDA and opioid receptor subsystems play in the emergence of acute and chronic tolerance to ethanol during adolescence (Sp.Aim 3)? And, finally, are the adaptive changes associated with chronic tolerance development causal for increasing ethanol consumption in adolescence (Sp.Aim 4)? The proposed work will not only provide convincing evidence as to whether the emergence of chronic tolerance to ethanol leads to increases in its consumption, but will also illuminate the relationships among acute, rapid and chronic tolerance and the role of tolerance development in contributing to the elevated ethanol consumption and the insensitivity to various aversive effects of ethanol characteristic of adolescence.